1. Field of the Invention
This invention relates to a fuel composition containing a normally liquid fuel such as a hydrocarbon fuel and ethanol and to methods that employ the fuel composition. The fuel composition and methods thereof provide overall improved performance for using the fuel composition in an internal combustion engine.
2. Description of the Related Art
Using ethanol in gasoline is well established around the world. Alternatively, ethanol is generally not used in diesel fuel due particularly to severe stability problems when water is present. The technology of mixing ethanol and diesel fuel has received much attention since the oil shortage crisis during the years between 1970 and 1980. However, ethanol-diesel fuel mixtures have suffered in a variety of performance areas: stability, corrosion, reduced power, lubricity, and low temperature properties. Ethanol-diesel fuel mixtures, especially in the presence of water and/or low temperatures, tend to be unstable resulting in separation to polar and nonpolar phases. The corrosive properties of ethanol were traced back to the instability of the mixture when exposed to contaminant water in the fuel delivery system. This stability problem resulted in the fuel pump and injection equipment being exposed to high concentrations of ethanol and water. Moreover, this mixture suffered from reduced combustibility properties when compared to a diesel fuel that was a conventional middle distillate fuel. The reduced combustibility is expressed as poorer start-up performance, reduced power and increased emissions. Reduced combustibility can be attributed, at least in part, to the lower BTU content of ethanol versus a middle distillate fuel. Thus, while the use of ethanol in diesel fuel systems can offer economic and environmental advantages from a renewable fuel point of view, the presence of water creates difficult technical problems involving storage and use of such fuels. Even if a small quantity of water gets into a diesel fuel containing ethanol, a polar phase containing ethanol will separate. The sources of this water can be the water that is difficult to remove from ethanol, or water that can be picked up by the ethanol-diesel fuel mixture from the environment. The problems associated with phase stability, which refers to the ability of the fuel to refrain from separating into component phases, can be addressed in principle by using either microemulsion or macroemulsion technology.
Hybrid fuel emulsions have been developed to improve the water tolerance of ethanol-diesel fuel mixtures in terms of phase stability so that these mixtures will remain in a single phase when exposed to water. Such emulsions include, for example, a mixture of diesel fuel, an alcohol, small amounts of water, and a surfactant system. A number of patents, including U.S. Pat. Nos. 6,129,773; 6,348,074; 4,477,258; 4,451,265 and International Publication Nos. WO 01/10982 A1 and WO 95/02654, describe surfactant systems containing long-chain fatty acids or derivatives thereof.
Various patents have published or issued which relate to emulsified fuel compositions and which specifically relate to compositions comprised of diesel fuel, water or ethanol, and surfactant. In International Publication No. WO 93/24593 and European Publication No. EP 117915 A2, alcohols (C1 to C12) are disclosed for use in water-diesel fuel or ethanol-diesel fuel mixtures to impart phase stability. Typical alcohols used were propanol, butanol, hexanol, and dodecanol.
The use of alkoxylated fatty alcohols and fatty acids as a stabilizing additive for diesel fuel containing ethanol has been disclosed in U.S. Pat. Nos. 6,306,184; 6,190,427; 6,017,369; and 6,348,074 and in International Publication Nos. WO 00/36055 A1; WO 01/62877 A1; WO 01/62876 A1; WO 01/44413 A2 and WO 01/10982 A1, and in U.S. Pub. No. US 2001/0003881 A1.
International Publication No. WO 02/068334 A1 discloses combustion modifiers for water-blended fuels, to include diesel fuels containing an alcohol, to reduce exhaust emissions of an internal combustion engine.
The present invention provides an ethanol-diesel fuel composition that contains a surfactant such that the fuel composition has excellent performance in terms of phase stability and lubricity. The present invention further provides improved performance in terms of exhaust emissions when a combustion improver is added to the fuel composition.